The present invention is directed to the field of manifold assemblies for use with heat exchangers, particularly heat exchangers for refrigeration applications.
Heat exchangers for refrigeration applications, particularly condensers and evaporators, are subjected to relatively high internal refrigerant pressure. Further, such heat exchangers cannot allow any leakage of refrigerant into the atmosphere and therefore preferably are designed with as few manufacturing connections as possible. Where manufacturing connections are necessary, their joints must be able to be manufactured economically and with a high probability that they will not leak.
Automotive condensers have typically been constructed with a single length of refrigerant tube, assembled in a serpentine configuration with an inlet at one end and an outlet at the other end. In some cases, two or more of such serpentine coils are assembled into an intertwined configuration so as to provide a multiple path flow of refrigerant across the air flow. The ends of the separate serpentine coils are connected to common manifolds. This concept of multiple path flow is extended to what is called a "parallel flow heat exchanger," in which all refrigerant tubes are straight and parallel to each other with the individual ends of these tubes connected to respective inlet and outlet manifolds. This configuration is commonly utilized in the construction of engine cooling radiators, oil coolers, and more recently, air conditioning condensers.
Condenser application to parallel flow has been more difficult to achieve in practice because of the need for multiple high pressure joints. Also, the atmospheric problems associated with release of standard refrigerants has necessitated the change to newer, more chlorinated refrigerants such as R-134A. The R-134A refrigerant is not as efficient as R-12 refrigerants, and also operates at higher pressure than R-12 refrigerants. The lower efficiency of the R-134A refrigerant requires a condenser design which not only is more efficient, such as a parallel flow design, but also is able to withstand higher internal operating pressures.
Manifolding multiple tubes to withstand high internal pressure can best be accomplished with a tubular manifold, the cross-section of which is circular for highest strength, as shown in FIG. 1. U.S. Pat. No. 4,825,941 Hoshino et al. is an example of such a manifold with a circular cross-section. The chief disadvantage to the tubular manifold with a circular cross-section is the difficulty of piercing the series of holes in each manifold to receive the multiple parallel refrigerant tubes. Also, the tubular manifold with circular cross-section presents difficulties in assembly during manufacture. One partial solution to these problems is to flatten one side of each manifold tube as shown in FIG. 2, so as to provide a D-shaped cross-section which can more easily be pierced and subsequently assembled. However, insertion of the tubes into the manifold is still difficult. Also, in some heat exchanger designs, it is necessary to insert baffles in each manifold to create a multiple pass refrigerant flow. Insertion of the baffles into a tubular manifold can also present difficulties in assembly during manufacture.
Accordingly, it has been proposed to use a two-piece manifold comprising a tank and a header plate. In one such construction, shown in FIG. 2 of U.S. Pat. No. 4,938,284to Howells, the tank is formed with inwardly facing grooves and the tank is slid into engagement with the header plate, which is planar. As shown in FIG. 5 of the Howells patent, the tank can alternatively be formed with inwardly curved side wall members and the header plate can be formed with upturned longitudinal edges for gripping engagement with the side wall members of the tank when the tank is slid into engagement with the header plate. In both constructions, the tank is coated before assembly with a brazing material and flux to enable it to be secured upon assembly to the header plate.
Although the constructions shown in the Howells patent provide both a mechanical and metallalurgical bond between the tank and header plate, sufficient clearance must be provided between the tank and the header plate to permit sliding of the one onto the other. This clearance prevents the good fit required for effective brazing. Further, it is often desirable to provide baffles in the assembled tank and header plate to adjust the flow path. When the tank and header plate are assembled by sliding, it is difficult, if not impossible, to place baffles between them prior to assembly.
In another construction, the tank is provided with a flange, tabs are placed on the header plate, a gasket is inserted between the header plate and the tank, and the tabs are crimped over the tank flange. Examples of such a construction are shown in U.S. Pat. No. 4,455,728to Hesse, U.S. Pat. No. 4,531,578 to Stay et al., and U.S. Pat. No. 4,600,051to Wehrman. A leakproof-type seal is provided by compressing the gasket. However, compression of the gasket is not sufficient to seal the header plate and tank under the high pressures found in condensers.
A solution to these problems was proposed in co-pending U.S. application Ser. No. 503,798 of Calleson, which is expressly incorporated herein by reference. In the Calleson application, a pair of opposed parallel shelves are formed in the inner wall of the tank inwardly of the bottom edges to define a pair of flanges extending from the shelves. The shelves in the tank form stops against which the header plate abuts. The tank flanges are crimped inwardly to engage at least a portion of the edge portions of the header plate along the entire length of the header plate. Also, the tank and header plate are brazed together along substantially the entire lengths of their mating surfaces in order to provide both a mechanical and a metallurgical bond which provides the strengths to withstand high internal pressures. A pair of opposed, longitudinally-extending horizontal ribs can be formed in the inner wall of the tank and provided with opposed slots to receive baffles, in order to adjust the flow pattern. The horizontal ribs can also serve as tube stops.
Although the crimped flange proposed in the Calleson application is superior to the prior art flange and tab configurations, the crimping of the flange around the header plate prevents the filler material or alloy from flowing well enough to provide as uniform or consistent a brazed joint or fillet as is ideally desired for high pressure applications. It is the solution of the above and other problems to which the present invention is directed.